D.-H. Ko

Thermal stability and structural characteristics of HfO2 films on Si (100) grown by atomic-layer deposition

The thermal stability and structural characteristics for gate stack structure of HfO2 dielectrics deposited by atomic-layer deposition (ALD) were investigated. The structural characteristics and chemical state of the HfO2 films in relation to the film thickness and postannealing temperature were examined by x-ray diffraction and x-ray photoelectron spectroscopy. An interfacial layer of hafnium silicate with an amorphous structure was grown on the oxidized Si substrate at an initial growth stage. The structural characteristics of the HfO2 films are closely affected by the interfacial layer and are depended on the thickness of the films. The 45 A thick HfO2 film with an amorphous structure was changed into a polycrystalline structure after rapid temperature annealing of 750 °C for 5 min, while thicker films were grown into a polycrystalline structure of monoclinic or tetragonal crystal structure. The silicate layer grown at the interfacial region is not stable even at 700 °C under ultrahigh vacuum condition...

Dielectric characteristics of Al2O3–HfO2 nanolaminates on Si(100)

The structural characteristics and the chemical state of a HfO2–Al2O3 nanolaminate structure, depending on the postannealing temperature, were examined by x-ray diffraction and x-ray photoelectron spectroscopy. The structural stability is significantly enhanced up to 870 °C and so is able to sustain its amorphous and laminate structure. However, the laminate structure is drastically broken at the annealing temperature of 920 °C and the crystallization is locally generated. In particular, the formation of the interfacial layer during the postannealing treatment is effectively suppressed in the nanolaminated structure. The dielectric constant of the nanolaminate structure calculated from the accumulation capacitance increases from ∼10 to ∼17 as the annealing temperature increases. This change is closely related to the degree of the mixture composed by Al2O3 and HfO2.

Change in the chemical state and thermal stability of HfO2 by the incorporation of Al2O3

Al2O3 incorporated HfO2 films grown by atomic layer deposition were investigated using various measurement tools. The accumulation capacitance of the Al2O3 incorporated into HfO2 film increases as the postannealing temperature increases because of changes in interfacial and upper layer thickness and in interfacial stoichiometry. The core-level energy state of a 15 A thick film shows a shift to higher binding energy, as the result of silicate formation and Al2O3 incorporation. The incorporation of Al2O3 into the HfO2 film has no effect on silicate formation at the interface between the film and Si, while the ionic bonding characteristics and hybridization effects are enhanced compared to a pure HfO2 film. Any dissociated Al2O3 on the film surface is completely removed by a vacuum annealing treatment over 850 °C, while HfO2 contributes to Hf silicide formation on the surface of the film.

Structural transition of crystalline Y2O3 film on Si(111) with substrate temperature

Abstract Crystalline Y 2 O 3 films on Si(111) were grown by ionized cluster beam (ICB) deposition in an ultra high vacuum (UHV). The crystallinity of the films deposited at several different temperatures was studied using X-ray diffraction (XRD) and reflection of high-energy electron diffraction (RHEED), and the chemical states of the films was investigated using X-ray photoelectron spectroscopy (XPS). The transformation from monoclinic to cubic structure was observed upon the increase of the substrate temperature from 100°C to 500°C. The single crystal cubic structure was obtained at substrate temperatures over 500°C. The stoichiometry and binding state in the films were gradually changed to a cubic Y 2 O 3 structure with the increase of the substrate temperature. The transformation of the film structure from a monoclinic structure to a cubic structure was also observed by post annealing treatment in an oxygen ambient.

GROWTH STAGE OF CRYSTALLINE Y2O3 FILM ON SI(100) GROWN BY AN IONIZED CLUSTER BEAM DEPOSITION

We investigated the initial and epitaxial growth stage of Y2O3/Si(100) grown by reactive ionized cluster beam deposition, using x-ray diffraction (XRD), atomic force microscope, and reflection high-energy electron diffraction. We also investigated the crystalline structure of the films using transmission electron microscopy and XRD. The preferred growth direction of Y2O3 grown by an ion beam changed completely from the 〈111〉 to the 〈110〉 orientation in order to minimize the overall energy of the film as the substrate temperature increased. In addition to the kinetic energy of the deposited atoms, oxygen partial pressure and the substrate surface state also bear a relationship to the change in the preferred growth direction. The crystalline growth of Y2O3 film depends on the state of the surface at the initial growth stage, whether the Si surface was first exposed to oxygen or yttrium. In particular, the silicon oxide layer which formed on the Si surface during the initial growth stage played an important ...

Interfacial characteristics of HfO2 films grown on strained Si0.7Ge0.3 by atomic-layer deposition

The interfacial characteristics of gate stack structure of HfO2 dielectrics on strained Si0.7Ge0.3 deposited by atomic-layer deposition were investigated. An interfacial layer including GeOx layers was grown on a SiGe substrate, and the thickness of the GeOx layer at the interfacial layer was decreased after the annealing treatment, while SiO2 layer was increased. The ∼50-A-thick HfO2 film with an amorphous structure was converted into a polycrystalline structure after rapid annealing at temperature of over 700 °C for 5 min. The interfacial silicate layer was effectively suppressed by GeOx formation, while the silicate layer was formed after the annealing treatment. GeOx formation in an as-grown film resulted in a decrease in the accumulation capacitance and an increase in the oxide trap charge.

Phase change behavior in oxygen-incorporated Ge2Sb2Te5 films

Oxygen-incorporated Ge2Sb2Te5 (GST) films were deposited using ion beam sputtering deposition. Sheet resistance in films with 16.7% oxygen content decreased at a higher annealing temperature than that of undoped GST films, while resistance in films with an oxygen content of over 21.7% decreased dramatically at lower temperatures. X-ray diffraction patterns showed crystallization to face-centered cubic phase was suppressed. However, phase separation to a hexagonal structure was observed in films with an oxygen content of over 21.7%. Extended x-ray absorption fine structure data of Ge K edge showed Ge was bonded to O as well as Te. Moreover, a stoichiometric GeO2 phase was not observed, while phase separation into Sb2O3 and Sb2Te3 occurred. The results indicate Ge–Te bonds with oxygen are related to structural stability.

Nitridation for HfO2 high-k films on Si by an NH3 annealing treatment

The characteristics of nitrided HfO2 films suggest that the diffusion of Si from the Si substrate to the film surface is induced by annealing in an NH3 ambient and that the incorporation of N is closely related to the diffusion of Si. Changes in the core-level energy state of the N 1s peaks of nitrided HfO2 films indicate that the quantity of N incorporated into the film drastically increases with increasing annealing temperature, especially at temperatures over 900°C. The incorporated N is mostly bonded to Si that diffused from the Si substrate into the film, while some N is incorporated to HfO2 at high annealing temperature. Some molecular N2 is generated in the film, which is easily diffused out after additional annealing. Moreover, the chemisorbed N in the film is not completely stable, compared to that at the interfacial region: i.e., the N in the film predominantly out diffuses from the film after additional annealing in a N2 ambient.

Structural and electrical characteristics of Y2O3 films grown on oxidized Si(100) surface

Heteroepitaxial Y2O3 films were grown on oxidized and clean Si (100) surfaces by ion assisted evaporation under an ultrahigh vacuum. The crystalline structure, crystallinity, morphology, and electrical properties were investigated using various techniques. The crystallinity assessed by x-ray diffraction and Rutherford backscattering spectroscopy shows that the films grown on the oxidized Si substrates have better crystallinity and smoother morphology compared to those on the clean Si. As the annealing temperature increases, the crystallinity and morphology are stable for the films grown on the oxidized Si, while those of the films grown on clean Si substrates degrade. The difference between the two films is attributed to the formation of hillocks and a chemical reaction at the interface between the film and SiO2. The low crystallinity, strain change, and the reaction of excess Y in the films grown on the clean Si contribute to the crystalline structure and the formation of hillock. These changes of crysta...

Structural characteristics of Y2O3 films grown on oxidized Si(111) surface

We investigated the characteristics of Y2O3 films grown on an oxidized Si(111) surface, using x-ray diffraction, Rutherford backscattering spectroscopy, and high-resolution transmission electron microscopy. The films grown on the oxidized Si show drastically improved crystallinity, compared with the film grown on clean Si surfaces: channeling minimum yield (Xmin) of 2.5% and full width at half maximum of rocking curve lower than 0.03°. The improvement of the crystallinity was due to the difference of the crystalline structure at the interface between the films grown on the oxidized and clean Si surfaces. Crystalline orientation of Y2O3 islands at the interfacial region was misaligned from the normal substrate direction. The misalignment decreased with increasing the substrate temperature. In particular, the ordering of the oxygen atom in the film grown on oxidized Si was improved compared to that of the Y atom, indicating that the crystallinity of the film is dominantly determined by the arrangement of th...